External appearanceColonial, with zooids wholly immersed. Colonies consist of upright, flat-topped fleshy lobes which are up to 2 cm in height. Common test grey and semi-transparent, sides and base coated with sand.The zooids are visible through the test of the colony (A. glabrum close-up).Larva unknown.

CharactersZooids coloured yellowish to orange; up to 10 mm in length; body divided into thorax, abdomen and post-abdomen. Oral siphon 6-lobed; atrial opening with languet bearing long median and small lateralprocesses. Branchial sac with 10-12 rows of 16-18 stigmata. Gutabdominal; stomach with continued or interrupted longitudinal folds. Gonads located in post-abdomen; with ovaries in the upper part and the male follicles forming a double row beneath them (A. glabrum zooid).

HabitatAttached to hard substrata; from low water line to about 400 metres.